In recent years, due to excellent light quality and high luminous efficiency, light emitting diodes have increasingly been used as substitutes for incandescent bulbs, compact fluorescent lamps and fluorescent tubes as light sources of illumination devices. Generally, a light emitting diode includes a substrate, an N-type semiconductor layer, an active layer and a P-type semiconductor layer arranged on the substrate in sequence. Light emitted from the active layer transmits to the outside.